A couple questions

Ok so I have about 30 ducks, mostly male, and haven't had time to separate most of the males from the females. All but one are welsh harlequin the only other one is a pekin. The pekin has always been good at laying her egg in the same spot unhidden. Well the males are at the point were they wanna breed, and I've seen them breed with mostly, of course, the pekin. Now she's hiding not only her eggs but two of the other ducks started laying and she's hiding them to.

So here's my questions. We were out of town for three days, the guy who was going to feed/water/ collect eggs couldn't find anything, we come home and oh, Harley has them of course, do you think they are developed enough to incubate? It's been about a month or two of them breeding before they started laying again this year.

Question #2 another egg I candled from last week, I was bored and home alone, looked like it was fertile. How long can an egg sit out (not in fridge) and still be able to incubate?

Last question, I'm building an incubator, what temps/ humidity should I keep it at? And when can I tell if they are developing?

I am not a hatcher, so cannot advise some of your questions, but I have a real concern for your females. Especially since some drakes will gang up on them. Please be sure to protect all members of your flock.

Ok, first, if the ducks are mating, then their eggs can be incubated. You can candle around day 5 and usually see veining to know that they are developing, if a drake ferilized the egg. Day 5 is early, but for sure by day 7-10.
You can not tell if an egg is fertile by candling, if it has not been incubated. The only way to tell that is to crack it open and examine the spot on the yolk, looking for a bullseye, but then of course you can't incubate that egg. If she was sitting on the eggs, it still takes about 5 days to be able to see good veins.

So, if they are mating, put some in the incubator, candle in a few days, and you'll know.

Unrefrigerated eggs are usually ok to incubate up to around about 10-14 days old. Some folks have had success with older eggs, even up to a month old, but most folks say 2 weeks or less is best.

Temps/humidity for incubating... 99.5-100 degrees with a fan, 101.5-102 without a fan is most successful for most people. Measured at the top height of the egg. Humidity depends alot on your local conditions, but for ducks eggs, I start around 30-35% RH and watch air cells throughout incubation for proper growth and adjust if necessary. Ventilation is also an important factor, so if you are building one, be sure to add some vent holes.

And we are planning on separating most if not all the males out to a different enclosure very soon we just haven't had the time. I did build the incubator so thanks so much for the temp and humidity numbers!